Recently, the size of such molding machines has been enlarged, thereby requiring that the associated die-clamping apparatus have a large clamping force. On the other hand, it is desirable that the operation speed be increased in order to improve the manufacturing yield. With the trend to the larger sizes of such molding machines, there is a great need for reducing the installation area required by the larger machines.
A die opening/closing method, which has been mainly employed, is so arranged that the two dies are moved forwardly/rearwardly at a high speed by a small drive force to predetermined positions by using a long cylinder having a small diameter, the tie bar and the movable die plate are fastened to each other in the realized die-closed state where the two dies have come close to each other, and then a short cylinder having a large diameter is used to strongly clamp the dies. Since the operational capacity of the hydraulic cylinder is small enough according to the aforesaid method to improve the responsiveness of the hydraulic pressure, the cycle time can be shortened. Furthermore, the capacity of the hydraulic fluid supply tank can be reduced and therefore the area required to install the machine can be efficiently reduced. Therefore, a variety of inventions relating to the aforesaid method have been disclosed in recent years. Some of the inventions of the aforesaid type will now be described.
Conventional Example 1 (FIG. 9) has been disclosed in Japanese Published Examined Utility Model Application No. (Y2) 61-26028. According to that document, one end of a tie bar 304 is integrally formed with a piston 303 of a die-clamping hydraulic cylinder 302 fixed to a stationary die plate 301, while another end of the tie bar 304 is supported by a support plate 305. The tie bar 304 has a threaded portion 304a which receives a half nut 307 fitted to a movable die plate 306 so as to clamp the tie bar 304 and the movable die plate 306. The die opening/closing operation to be performed by the movable die plate 306 is effected by a hydraulic opening/closing cylinder 308 disposed between the two die plates 301 and 306. The top and the bottom surfaces of the threaded portion 304a of the tie bar 304 do not have the threads, so that the guiding of the opening/closing operation of the movable die plate 306 is performed by the aforesaid top and bottom surfaces having no threads. The clamping of the dies is accomplished by the tie bar 304 being clamped by the half nut 307 of the movable die plate 306, and then the die-clamping hydraulic cylinder 302 being used to draw the tie bar 304 along with the support plate 305. At this time, the support plate 305 supports the other end 304b of the tie bar 304 while sliding on the bed. The adjustment of the die-clamping range is performed at the time of changing the die, in a manner corresponding to the thickness of the subject die, by using region 304a of the tie bar 304 having the threads formed on the surface thereof. However, the deviation corresponding to the thread pitch must also be corrected. Therefore, the deviation is corrected in such a manner that the tie bar 304 is, together with the support plate 305, moved by an electric motor 309 to align the engagement position.
Conventional Example 2 (FIG. 10), which has been arranged so as to improve the Conventional Example 1 and which has been disclosed in Japanese Published Examined Utility Model Application No. (Y2) 61-26028, is constituted in such a manner that one end of a tie bar 321 is integrally formed with a piston 323 of a die-clamping cylinder 322 and has the shape of a perfect cylinder (i.e., having no threaded portion). The other end of the tie bar 321 is secured to a support plate 324. A tie bar penetration hole 325a, formed in a movable die plate 325, has a hydraulic clamping device 326 secured therein so as to secure the movable die plate 325 and the tie bar 321 at an arbitrary die-closing position which corresponds to the height of the die. Furthermore, die-clamping is so performed that the die-clamping hydraulic cylinder 322 drives the movable die plate 325 together with the tie bar 321 and the support plate 324 which is secured to the tie bar 321.
Conventional Example 3 (FIG. 11), which has been arranged so as to improve the Conventional Example 2 and which has been disclosed in Japanese Published Unexamined Patent Application No. (A) 1-232004, has one end of a tie bar 331 integrally formed with a piston located in hydraulic die-clamping cylinder chamber 337, and is constituted in such a manner that stopper rods 334 and 335 are disposed so as to quickly perform the alignment of the engagement position between a threaded portion 332 of a tie bar 331 and a half nut 333 for locking. Therefore, the clamping point of a movable die plate 336 can be assuredly determined.
Conventional Example 4 (FIG. 12), which has been arranged so as to improve the Conventional Example 3 and which has been disclosed in Japanese Published Examined Patent Application No. (B2) 2-9924, is constituted in such a manner that an engagement groove portion 346 for receiving a half nut 345 is formed at a front portion 344a of a tie bar 344, the other end of the tie bar 344 being formed integrally with a piston 343 of a die-clamping cylinder 342 provided for a stationary die plate 341. Furthermore, a die-closing end of the movable die plate 348 is restricted by a stopper 347, so that engagement can be assuredly carried out. In addition, in order to be adaptable to dies having various heights, the die-clamping cylinder 342 has a satisfactorily long stroke.
Conventional Example 5 (FIG. 13), disclosed in Japanese Published Unexamined Patent Application No. (A) 63-317243, is so arranged that a tie bar 352 is secured to a movable die plate 351, a die-clamping cylinder 354 including a double-rod type piston 353 having a hole 353a is included in a stationary die plate 355, a threaded portion 352a which is formed in the front portion of the tie bar 352 is received by a half nut 356, and the dies are clamped by the die-clamping cylinder 354. The deviation of the engagement position corresponding to the thread pitch, which has taken place at the time of aligning the heights of the dies, is corrected by shifting the piston position of the die-clamping cylinder 354 by a stopper leg 357 disposed on the back side of the die-clamping cylinder 354.
Conventional Example 6 (FIGS. 14 and 15), disclosed in Japanese Published Examined Patent Application No. (B2) 3-6880, is so arranged that the die-clamping apparatus is structured into a vertical apparatus, a tie bar 362 (a support column) is secured to a movable die plate 361 (an upper frame), and the tie-bar 362 is inserted into a hole formed in a double-rod type piston 364a having a hole of a die-clamping cylinder 364 secured to a stationary die plate 363 (a lower frame) so as to guide the forward/rearward movement of the movable die plate 361. A hydraulic clamping machine 365 (see FIG. 15) is included in the hole formed in the piston 364a, so that the tie bar 362 and the hydraulic clamping machine 365 are secured to each other and the dies are clamped in response to the application of oil pressure on piston 364a.
Conventional Example 7 (FIG. 16), disclosed in Japanese Published Examined Patent Application No. (B2) 1-49088, is arranged in such a manner that a tie bar 372 (a support column) is secured to a stationary die plate 371 (a lower frame), a hydraulic clamping machine 365 is included in a movable die plate 373 (an upper frame), and the tie bar 372 is inserted into a hole formed in a double-rod type piston 375 having a hole of a die-clamping cylinder 374 disposed on a movable die plate 373 so that the forward/rearward clamping movement of the movable die plate 373 is guided. The piston 375 includes a hydraulic clamping machine 365 so as to secure the tie bar 372 and the piston 375. Therefore, the movable die plate 373 is moved downwardly and die clamping is performed by the piston 375 in response to the application of pressurized oil thereto.
However, each of the aforesaid conventional examples encounters the following problems.
Conventional Example 1 (FIG. 9) raises a problem in that the aligning of the engagement position of the half nut 307 takes an excessive amount of time, the movable die plate 306 can easily be caught by the threads of threaded portion 304a because the tie bar 304 has no lateral stationary guide for guiding the movable die plate 306, and the insertion portion is too short. It is also difficult to form threads on the surface of the tie bar 304 because the threads are formed on only the right and the left surfaces. Furthermore, the arrangement wherein the tie bar 304 is integrally formed with the piston 303 of the die-clamping cylinder 302 will cause dimensional changes due to machining errors of the stationary die plate 301, the movable die plate 306, the tie bar 304, the support plate 305, and the like, due to a temperature difference, and due to the thermal stress resulting from the temperature difference. Accordingly, a gap must be present between the tie bar insertion hole formed in the movable die plate 306 and the outer surface of the tie bar 304, causing the die-clamping accuracy to deteriorate. What is worse, the movable die plate 306 cannot be moved smoothly if the temperature changes excessively.
Conventional Example 2 (FIG. 10) encounters a problem similar to that experienced with Conventional Example 1 in that the arrangement is made, similarly to Conventional Example 1, in such a manner that the tie bar 321 being integrally formed with the piston 323 of the die-clamping cylinder 322 will cause the dimensional changes due to the machining errors of the stationary die plate 327, the movable die plate 325, the tie bar 321, the support plate 324 and the like, due to a temperature change, and due to the thermal stress resulting from the temperature difference.
Conventional Example 3 (FIG. 11) encounters a problem which takes place because the insertion hole 336a of the movable die plate 336 and the threads 332 of the tie bar 331 undesirably interfere with each other. Furthermore, the die-clamping accuracy will easily deteriorate due to machining errors, due to the thermal stress resulting from the temperature changes, or due to deformations which take place as a result of a deviated load, and the like.
Conventional Example 4 (FIG. 12) is so arranged that the movable die plate 348 and the tie bar 344 are separated from each other, causing the size of the die-clamping cylinder 342 to be enlarged excessively. Therefore, the hydraulic control responsiveness deteriorates. Furthermore, the tie bar 344 is formed as a cantilever structure. Therefore, the front portion 344a inclines downwardly, causing a positional deviation from the insertion hole 348a to easily take place. What is even worse, a seal (omitted from illustration) of the die-clamping cylinder 342 can be easily damaged in actual use. In addition, the rigidity of the tie bar 344 does not substantially contribute to the deviated load at the time of the installation of the die to the movable die plate 348. Therefore, a guide means for guiding the movable die plate 348 must have satisfactory accuracy and rigidity, causing the cost to be raised and the required installation area to be enlarged excessively.
Conventional Example 5 (FIG. 13) is so arranged that the tie bar 352, which has been separated from the piston hole 353a of the die-clamping cylinder 354, is inserted into the piston hole 353a at the time of clamping the dies. Therefore, the deviated load due to the weight of the movable die 358 and that of the tie bar 352 and the gap of the die opening/closing guide portion for guiding the movable die plate 351 will deviate the center of the piston hole 353a and that of the tie bar 352 from each other, causing an interference to take place. What is worse, the die-clamping hydraulic cylinder 359 is positioned upwardly away from the die opening/closing guide portion for guiding the movable die plate 351. Therefore, the gap of the die opening/closing guide portion cannot be made constant because the movable die plate 351 is opened/closed by the die-clamping hydraulic cylinder 359. Hence the quantity of the inclination of the movable die plate 351 becomes too large, causing problems of damages of the piston 353 and the half nut 356 of the die-clamping cylinder 354 to arise due to the asynchronous action of the two die guides or the interference of the tie bar 352. Since the rigidity of the tie bar 352 does not substantially contribute to the deviated load, the portion for guiding the die opening/closing operation to be performed by the movable die plate 351 must have sufficient rigidity. Therefore, the cost cannot be reduced and the required installation area becomes too large.
In Conventional Example 6 (FIGS. 14 and 15), a large gap must be formed between the sleeve 365a of the hydraulic clamping machine 365 and the tie bar 362 to absorb the machining errors and the thermal deformation of the main frame and members of each of the stationary die plate 363, the movable die plate 361, the tie bar 362, and the like. In order to improve the durability, the gap must also be enlarged. Hence, the quantity of deformation of the sleeve of the hydraulic clamping machine 365 becomes too large, causing the force for clamping the tie-bar 362 and the sleeve 365a to be reduced. What is worse, the arrangement wherein the hydraulic clamping machine 365 is included in the piston 364a of the die-clamping cylinder 364 will cause a difficulty in that disassembly and repair cannot be easily performed.
In Conventional Example 7 (FIG. 16), the size of the piston 375 so arranged that the hydraulic clamping machine 365 is included in the movable die plate 373 become too large and the weight of the same becomes too heavy. Since the large and heavy piston 375 is included by the movable die plate 373, the weight of the movable member of the movable die plate 373 becomes very heavy. Hence, controls of the acceleration and deceleration of the operations of opening/closing the dies cannot easily be performed due to the excessively heavy weight of the movable member. Furthermore, the fact that a large quantity of oil must be supplied to the die-clamping cylinder 374 and that the die-clamping cylinder 374 is included in the movable die plate 373 will cause the diameter of a rubber hose (omitted from illustration) to be enlarged. Hence, the bending radius and the operational range becomes too large, causing a problem to arise in that the size of the machine cannot be reduced. As a result, maintenance cannot be performed easily and the appearance deteriorates. In addition, problems similar to Conventional Example 6 arise in that the realized durability and the clamping force of the hydraulic clamping machine are unsatisfactory, and disassembly and repair cannot be performed easily.
As can be understood from the above description, the dimension changes of the stationary die plate, the movable die plate, the tie bar, the support plate, and the like, which take place due to the machining errors and the thermal stress resulting from the temperature difference will cause problems in that the alignment cannot be realized or the accuracy deteriorates since a large gap is formed. In addition, the arrangement so made that the hydraulic clamping machine is included by the piston of the die-clamping cylinder will hamper disassembly and repair. Consequently, they are not suitable to serve as a die-clamping apparatus.